Onboard vapor recovery system with two-stage shutoff valve

ABSTRACT

An onboard vapor recovery system for a vehicle fuel system having a fuel tank (10), a filler neck (12) dynamically sealed by high pressure fuel flow from a filler nozzle, and a vapor recovery apparatus such as a carbon canister (18). The system preferably uses an inventive liquid level operated control valve (20) which shuts off refueling with a two-stage closing operation providing an initial soft shutoff and a final shutoff. The system also preferably includes a valve (22) in the fuel tank to maintain a predetermined pressure head sufficient to hold the system closed against further refueling at least temporarily, and a positive action, one-way check valve (24) in the lower end of the filler pipe (12) to prevent spitback of fuel from the pressurized tank (10) once refueling has ceased.

RELATION TO PRIOR APPLICATION

This application is a division of U.S. patent application Ser. No.08/295,196 filed Aug. 24, 1994, now U.S. Pat. No. 5,590,697.

FIELD OF THE INVENTION

The present invention relates generally to "onboard" type fuel vaporrecovery systems for vehicle fuel tanks, wherein fuel vapor generatedduring the refueling process is vented to onboard vapor recoveryapparatus such as a carbon canister.

BACKGROUND OF THE INVENTION

Systems for controlling the flow of fuel vapor from a vehicle fuel tankto a recovery apparatus such as a carbon canister are generally known. Acommon approach is to place a control valve in series between the fueltank and the vapor trap to selectively open and close the vapor ventingpathway in response to changes in vehicle refueling activity.

Some known vapor control valves open or close in response to pressureconditions at the filler pipe inlet, for example when a filler pipe capis removed or replaced to indicate the start or finish of refuelingoperations.

Other pressure-operated control valves respond to vapor pressure in thefuel tank itself to open, close, or adjust the rate at which fuel vaporis vented.

Another known type of valve responds to the level of liquid fuel in thetank, staying open to vent vapor as long as the fuel level is below apredetermined level. These are sometimes referred to as "fill control"or "shutoff" valves, since their closing creates a sudden pressureincrease in the tank which prevents further refueling.

Prior vapor recovery systems often use pressure-operated control valves,sometimes supplemented with rollover and/or fill control valves tosupplement the pressure operated vapor control. Disadvantages of suchpressure-operated systems include their relative complexity and cost;their sensitivity to changing pressure conditions in the fuel system;and, the need for vapor seal and/or signal structure in the filler pipe,for example filler nozzle trap doors and signal pressure lines toprevent the loss of fuel vapor to the atmosphere during refueling and/orto provide signal or actuation pressure to the control valve.

One known technique for eliminating filler nozzle trap door or otherseal structure in the filler pipe is to create a "dynamic" seal in thepipe using only the flow effects of a high velocity stream of fuel fromthe filler nozzle. By properly shaping the filler pipe in the regionwhere the filler nozzle is located during refueling, and pumping thefuel at high velocity, a vacuum or draw-type seal can be created andmaintained around the filler nozzle during refueling. This eliminatesthe need for seal door and similar structure. However, manypressure-operated control valves cannot function without such structurein the filler pipe. The dynamic sealing generates higher refuelingpressure in the tank, tending to cause undesirable fuel expulsion or"spitback" from the filler pipe inlet at the end of the refuelingoperation. The prior art has not adequately addressed the need for anonboard vapor recovery system suitable for high pressure refueling witha dynamic filler pipe seal.

SUMMARY OF THE INVENTION

The present invention in a first form is an onboard vapor recoverysystem for a vehicle fuel system including a fuel tank, a vapor trap,and a filler pipe using a "dynamic" seal induced by high velocityrefueling from the filler nozzle. In general, the system of the presentinvention includes a complementary arrangement of a fuel levelresponsive control valve in the fuel tank for venting fuel vapor to thetrap when the liquid fuel level is below a predetermined level, aseparate valve capable of maintaining a sufficiently high pressure headin the fuel tank when the control valve is closed to defeat therefueling pressure, and a check valve in the lower end of the fillerpipe which opens for refueling and which positively closes against thepressure in the fuel tank after the refueling operation to preventspitback.

The system preferably includes bleed means such that the head pressureis only temporarily maintained when the system is closed, for examplelong enough to prevent further refueling attempts immediately after thetank has been filled. The pressure head maintaining valve canincorporate the bleed means, and preferably includes rollover valvemeans.

The invention in a further form is a fuel level responsive control valvecomprising a two-stage shutoff valve with a cushioned, "soft" initialshutoff for the high pressure refueling operation. In one embodiment thecontrol valve includes primary and secondary venting ports successivelyclosed by first and second valve structure at first and second fuellevels. In the presently claimed embodiment, the shutoff valve comprisesan offset shutoff valve with radially offset primary and secondary ventports and associated valve structure. As will be apparent to thoseskilled in the art, this two-stage shutoff valve is especiallywell-suited for the inventive fuel system described above, although ithas utility used alone or in different systems. These and other featuresof the invention will become apparent upon further reading of thespecification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a vehicle fuel system with anonboard vapor recovery system according to the present invention;

FIG. 2 is a section view of a coaxial fuel level responsive controlvalve employed in the system of FIG. 1, claimed in a separateapplication;

FIG. 2A illustrates the valve of FIG. 2 in a fully closed condition;

FIG. 3 is a section view of an alternate, presently claimed offsetcontrol valve useful for the system of FIG. 1;

FIG. 3A is a section view of the valve of FIG. 3 in a fully closedcondition;

FIG. 4 is a section view of a rollover valve for use with the system ofFIG. 1;

FIG. 5 is a section view of a liquid seal check valve for use in thefiller pipe of FIG. 1;

FIG. 5A illustrates the valve of FIG. 5 in an open condition; and

FIG. 6 illustrates the system of FIG. 1 during a refueling operation.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring now to FIG. 1, an onboard vapor recovery system according tothe present invention is shown for a vehicle fuel system comprising atank 10, a filler pipe 12 with an inlet 14 selectively closed by cap 16,and a vapor canister 18 connected to tank 10 by a vent line 17. Thefiller pipe in the inventive system is configured to create a dynamicseal with a filler nozzle during refueling; i.e., fuel pumped at highvelocity from the filler nozzle into the filler pipe creates avacuum-type seal adjacent the filler nozzle outlet to prevent the escapeof fuel vapor out the filler pipe inlet. In the illustrated embodimentthe dynamic seal results in fuel being introduced into the tank at apressure head of approximately eighteen to twenty inches of waterpressure. Prior systems without dynamic sealing often operate atrefueling pressures of around seven to ten inches.

Fuel vapor from tank 10 is vented through line 17 to canister 18, whereit is adsorbed and periodically purged to the engine for combustion.Fuel vapor venting from tank 10 via line 17 to canister 18 is through afuel level responsive control valve 20 (FIG. 2) or 120 (FIG. 3), mountedin a suitable aperture in the fuel tank to be closed by liquid fuel ator above a predetermined level shown at 11. When the liquid fuel level11 in tank 10 is below that predetermined level, valve 20 remains opento vent fuel vapor to canister 18.

In the illustrated embodiment control valve 20 (or 120) substantiallyreduces, but does not abruptly halt, vapor venting from the tank to thevapor canister when an approximate full fuel level is reached. Instead,valve 20 provides a limited amount of additional, low volume vaporventing between a first full level and a slightly higher maximum "roundoff" level. This results in an initial "soft" shutoff at the first fulllevel to prevent overly rapid backup of fuel in the filler pipe andpossible spitback onto the person operating the filler nozzle. When theinitial shutoff occurs, the resulting rise in tank pressure forces fuelback up the filler pipe to cover the mouth of the filler nozzle,activating an internal shutoff mechanism in the filler nozzle in knownmanner. After a short time the fuel standing in the filler pipe drainsback into the tank. If the nozzle operator continues to fill the tankafter being cued by the initial shutoff, the valve closes at the maximumlevel to trigger a final shutoff and end the refueling activity.

The system of the present invention also includes a rollover-type headvalve 22, in the illustrated embodiment of FIG. 1 a separate valve 22mounted in the fuel tank to vent fuel vapor to canister 18 through line23. Rollover head valve 22 is designed to maintain a sufficient pressurehead in the vapor space of the fuel tank after valve 20 has closed forfuel to accumulate in the filler pipe for nozzle shutoff. For example,head valve 22 maintains approximately twenty inches of water pressure.Below this pressure rollover head valve 22 remains closed; above thispressure rollover head valve 22 opens to rapidly vent fuel vapor tocanister 18. In the illustrated embodiment of FIG. 1, rollover headvalve 22 includes a small bleed orifice or vent, for example on theorder of 0.020 inches diameter, to provide a low volume, continuous ventfrom the fuel tank to the canister. As described below, the bleed invalve 22 provides sufficient head valve function on its own if pressurereduction after fill occurs within a reasonable time.

Still referring to FIG. 1, the system of the present invention alsoincludes a one way, low back pressure, liquid seal check valve 24 in thelower end of the filler pipe at or below the full fuel level. Highvelocity fuel introduced from the upper end of the filler pipe duringrefueling forces check valve 24 open to fill the fuel tank. When controlvalve 20 closes to seal the tank and refueling ceases, check valve 24positively closes against the pressurized fuel in the tank to prevent itfrom being expelled out the filler pipe.

The one way nature of check valve 24 prevents its being forced open forreverse fluid flow from the tank to the filler pipe.

Vacuum relief for the fuel tank is provided by suitable vacuum reliefstructure 15 in cap 16 of a known type, acting in series with checkvalve 24. For example, if negative pressure conditions occur in thevapor space in tank 10, the pressure imbalance across check valve 24will cause it to open, relieving the tank with pressure stored in fillerpipe 12. If this residual pressure is not enough to relieve the tankvacuum, the vacuum relief valve structure 15 in cap 16 will additionallyopen to provide atmospheric relief pressure through pipe 12 and checkvalve 24 to the tank. This arrangement complements the inherent vacuumrelief structure in either of valves 20 or 22. The bleed in valve 22 mayprovide some vacuum relief prior to relief through cap 16; and vacuumrelief can sometimes occur across the float structure in valve 20, whichcan be forced downwardly against liquid fuel if the vacuum pressuredifferential across it is high enough.

FIG. 1 illustrates the vehicle fuel system immediately after the tankhas been filled to the maximum level and refueling has ceased. In thiscondition control valve 20 is closed, rollover head valve 22 is closed(assuming a pressure head in tank 10 at or below the pressure relieflevel of the rollover head valve), and check valve 24 is closed. Acolumn of liquid fuel (not shown) may remain standing in the filler pipeabove the check valve. Except for the low volume bleed vent in rolloverhead valve 22, the entire system is closed.

The low volume bleed vent in rollover head valve 22 dissipates theclosed system pressure to the canister, maintaining the pressure headfor a short time (for example, less than a minute) after the check valve24 and shutoff valve 20 have closed. Temporarily maintaining the closedsystem pressure head in this manner discourages attempts at overfillingfor a reasonable period, and then allows tank pressure to decay so thatstanding fuel in the filler pipe can drain into the tank and overallsystem pressure is reduced.

Should tank pressure increase in this closed system condition beyond thecapacity of the bleed vent, for example if the vehicle is left parkedwith the tank at maximum fuel level and at high temperature, therollover head valve 22 opens for rapid venting until the excess pressureis relieved. In this extreme case, the tank pressure will notsignificantly exceed the twenty-inch head maintained by the head valve,although some hysteresis in pressure reduction may initially occurdepending on the exact rollover structure used.

It should be noted that the check valve 24 will remain closed by thespring and the high fuel level if the cap is removed, preventing fuelexpulsion. If the vehicle is driven in this closed-system condition,fuel sloshing will intermittently open shutoff valve 20, which willrapidly reduce tank pressure.

A vent line 21 from valve 20 to the atmosphere provides emergencypressure relief in a manner described below in reference to FIG. 2.

The control valve 20 is open both during refueling and normal vehicleoperation, so long as the fuel level in the tank is below the maximum(i.e., reopening) level, which those skilled in the art will recognizeas varying slightly as the result of different tank pressures and theeffects of hysteresis. Vapor is accordingly vented to the canister 18 ona relatively continuous basis. To prevent saturation of the canisterwith fuel vapor, an electronic purge solenoid 19 is connected downstreamfrom the canister to periodically allow vacuum from the vehicle intakemanifold to "purge" vapor from the canister to the engine.

It can be seen from the foregoing that the fuel level responsive controlvalve 20, head valve 22 and check valve 24 provide complementary vaporrecovery, shutoff and spitback-prevention in a manner uniquelycoordinated for high pressure refueling with a dynamically-sealed fillerpipe. Fuel level responsive valve 20 (120) is unaffected by pressureextremes and vents freely until the tank is filled, at which point itscushioned shutoff provides a first level of spitback protection againstthe high pressure refueling. Head valve 22 maintains the high pressurehead needed in the tank to provide a shutoff-inducing back pressureafter valve 20 has closed, at least long enough to discourageoverfilling attempts, and then reduces overall pressure with acontrolled bleed. Check valve 24 provides an immediate, reliable checkagainst spitback from the tank pressure accumulated for the shutofffunction. Check valve 24 also maintains a back pressure low enough toavoid premature shutoff of the filler nozzle.

Referring now to FIGS. 2 and 2A, a first embodiment of a shutoff typecontrol valve suitable for the system of FIG. 1 is illustrated. Valve 20comprises an essentially hollow valve body mounted in a suitableaperture in the fuel tank. Lower half 42 of the valve is located in theinterior of the fuel tank, and communicates with an upper half 44outside the fuel tank. The valve is fastened to the fuel tank in liquid-and vaportight manner by connector flange 46, for example by hot platewelding, ultrasonic welding, grommet-type seal or other knowntechniques.

Lower half 42 of valve 20 defines a float chamber 48 open at its lowerend to receive liquid fuel as the fuel level in the tank rises to thefull level. Radial vent ports 43 and holes 47 in the bottom end of lowerhalf 42 provide vapor and liquid communication between tank 10 and floatchamber 48. At its upper end float chamber 48 includes a primary ventport 50 opening into the upper half 44 of the valve and communicatingwith an outlet 52 connected by conduit or hose 17 (FIG. 1) to vaporcanister 18.

Valve 20 can be provided with baffle structure (not shown) associatedwith vent ports 43 in chamber 48, to prevent liquid fuel from splashingthrough vent ports 43 to port 50.

Chamber 48 also includes a pressure relief port 54 at its upper end,opened and closed by spring-biased pressure relief valve 56 toselectively vent chamber 48 to a pressure relief outlet 58 connected tothe atmosphere (by line 21 in FIG. 1).

A fuel level responsive float 49 is contained in chamber 48 for up anddown movement on guide pins 49a as the float chamber fills with liquidfuel through holes 47 and vents 43. The density of float 49 is balancedrelative to that of the fuel, for example with a spring 49b, such thatit closes when immersed in liquid fuel in both upright and rolloversituations. Float 49 may have a density less than, equal to, or greaterthan that of the fuel, balanced by spring 49b as desired for fillcontrol and rollover function.

Referring to FIGS. 2 and 2A, the upper end of float 49 is connected byspindle 49c to a first valve cage 60 defining a cylindrical cupcontaining a primary shutoff valve element 62. Primary valve element 62is axially trapped in cage 60 by interference between its shoulder 64with lip 61 on cage 60. Valve element 62 includes a number of ventapertures 66 which allow vapor communication between float chamber 48and the interior of valve cage 60. Valve element 62 also includes acentral vent passageway 68 aligned with vent port 50. Primary valveelement 62 is normally forced against lip 61 at the upper end of cage 60by a spring 70. Valve element 62 supports a sealing member 72 at itsupper end, for example a resilient rubber-like disc retained by anangled collar 69.

A second valve cage 74 is formed inside valve cage 60, containing asecondary valve disk 76. Valve cage 74 comprises a plurality ofactuation fingers 78 of varying height around the periphery of valvedisk 76. Valve disk 76 is free to move axially within cage 74 betweenthe upper ends of fingers 78 and a centering bead. Second valve cage 74and secondary valve 76 can comprise, for example, peeling action valvestructure of the type shown and described in U.S. Pat. No. 4,753,262 toR. Bergsma, co-owned by the assignee of this application.

In operation, float 49 and the primary and secondary valve elements 62,76 remain in a lower position in float chamber 48 away from primary ventport 50 whenever the fuel level is below a predetermined level.

When the fuel reaches a predetermined near-full level, float 49 rises inchamber 48, forcing seal 72 on primary valve element 62 against theprimary vent port 50.

This closes primary vent port 50, but leaves open the lower volumeventing from chamber 48 through valve cage 60 via apertures 66 andpassageway 68 in valve 62. The result is a significant reduction in therate of vapor venting, causing a rapid but controlled rise in the tankhead pressure. This in turn forces fuel back up the filler pipe at acontrolled rate, actuating the filler nozzle mechanism for an initial"soft" shutoff without spitback onto the operator.

The initial shutoff is a cue to the operator that the tank is close tofull. At this point primary valve 62 is in the position shown in FIG. 2,above valve disk 76 resting in cage 74, held in place by the force ofspring 70.

After the initial soft shutoff and the shutoff-inducing rise in tankpressure, vapor pressure in the tank is dissipated fairly quickly, forexample in a few seconds, through the secondary vent path defined byapertures 66 and passageway 68. This allows the fuel backed up in thefiller pipe to drain into the tank. As a result, a small amount ofadditional fuel can be added to round off the tank by "clicking" thefiller nozzle operating handle.

If the nozzle operator should choose to add fuel after the initialshutoff, float 49, cage 60 and cage 74 are forced upwardly by the risingfuel against spring 70 until valve disk 76 contacts and closes offcentral passageway 68 in valve 62 as shown in FIG. 2a. This completelycloses venting from the fuel tank through valve 20 to canister 18, andresults in a final shutoff cue to the filler nozzle. Should the operatorignore these shutoff indications and unwisely persist in trying to addfuel beyond the initial shutoff cue, and somehow override or circumventthe filler nozzle shutoff mechanism and the few round-off "clicks"allowed before final shutoff, the fuel will simply back out the fillerpipe inlet.

The two-stage soft shutoff with its cushioned initial shutoff andcontrolled round-off allowance can be adjusted as desired through therelative sizing of the primary and secondary vent ports or passages,spring forces, the relative height of the first and second valvescontrolling the amount of round-off, and in other ways which will beapparent to those skilled in the art. In the illustrated embodiment theprimary and secondary valve 62, 76 are calibrated to permit three orfour clicks of round-off before completely closing the valve.

Valve 20 remains fully closed until the level of liquid fuel in the tankdrops, with valve disk 76 first being peeled off passageway 68 byfingers 78 as float 49 drops, followed by valve 62 being pulled fromvent port 50 by valve cage 60 as the float drops further.

Pressure relief valve 56, located above the maximum fuel level, isforced open against spring 57 when vapor pressure in the tank exceeds apredetermined safe level, for example sixty inches water pressure. Valve56 would then open to reduce tank pressure to a safe level. Theinfrequency and nature of emergency pressure venting warrants ventingvalve 56 to the atmosphere for immediate pressure reduction.

FIGS. 3 and 3A illustrate an alternate, presently claimed two-stage softshutoff valve 120 suitable for the system of FIG. 1. Its operation issimilar to that of the valve in FIG. 2, but the primary and secondaryvalves are radially offset, rather than coaxially arranged.

In FIG. 3 a primary vent port 150 and a secondary vent passage 168 areradially spaced from one another at the upper end of float chamber 148.Vents 150, 168 vent vapor from the tank to the upper half 144 of valve120, where it passes to a vapor trap through outlet 152. Spring balancedfloat 149 supports a primary valve 162 for closing primary vent 150, anda secondary valve 176 for closing passageway 168. Primary valve 162 isnormally positioned higher than valve 176 by bias spring 170.

Secondary valve 176 may, for example, be the peel-away type illustratedin U.S. Pat. No. 5,313,977 to Bergsma et al, co-owned by the assignee ofthe present application, including a valve element 178 and peel-awaystructure 180.

Float 149 and valves 162, 176 remain below the vent ports 150, 168 aslong as liquid fuel is below the full or near-full level. When fuel infloat chamber 148 reaches the predetermined "soft" shutoff level throughradial and/or axial ports 143, 147 in lower half 142, float 149 isforced upwardly to initially close primary vent port 150 with valve 162.This initiates the initial soft shutoff described above. If the operatoradds additional fuel by clicking the filler nozzle, float 149 is liftedfurther against spring 170 until second valve 176 contacts and closesoff the secondary passageway 168 as shown in FIG. 3A. This finalizes theshutoff of control valve 120 in the manner described above in FIG. 2.

Valve 120 opens in a manner similar to valve 20 described in FIG. 2;i.e., valve 176 is first peeled off passageway 168 by the descendingfloat, followed by valve 162 being pulled away from primary vent outlet150 as the fuel level drops further. It will be apparent to thoseskilled in the art that, despite the different structure, valve 120 inFIG. 3 achieves a two-stage soft shutoff similar to that of valve 20 inFIG. 2. It is therefore suitable for use with the system of FIG. 1 inplace of valve 20. It will also be apparent to those skilled in the artthat such a valve has utility apart from the system of FIG. 1, eitheralone or in a different system. For example, valve 120 is useful for anyonboard vapor recovery application where a two-stage, liquid-responsiveclosure with initial "soft" shutoff is desired.

FIG. 4 illustrates one embodiment of a rollover-type head valve 22suitable for use in the system of FIG. 1. Rollover head valve 22comprises an essentially hollow body mounted to the fuel tank 10 througha suitable aperture via a shoulder portion 22b and resilient sealmembers 22c and 22d. Rollover head valve 22 has an upper half 22elocated outside the tank and including an outlet 22f connected to thevapor canister as shown in FIG. 1 by suitable hose or conduitconnection. A lower half 22g of the rollover head valve extends into thefuel tank, and includes a rollover float chamber 22h. At its upper endfloat chamber 22h communicates with outlet 22f by way of a rollover ventoutlet 22i and a head valve vent outlet 22j. Rollover vent outlet 22i isselectively closed by a spring balanced rollover float valve 22k held infloat chamber 22h, and head valve vent outlet 22j is normally closed bya ball-type head valve 22l. Float chamber 22h includes a number ofradial vent ports 22m through which fuel vapor from the tank can enterfloat chamber 22h and pass through vent outlets 22i, 22j to rolloverhead valve outlet 22f and the vapor canister. Float chamber 22h alsoincludes a hole 22n in its end plate 22o through which liquid fuelenters the float chamber to raise float 22k when the liquid level in thetank rises to the level of rollover head valve 22.

Further explanation of the structure and operation of a rollover valvesimilar to 22k and a head valve similar to 22l is found in U.S. Pat.Nos. 5,313,977 to Bergsma et al and U.S. Pat. No. 5,253,668 to Mills,respectively, both co-owned by the assignee of this application.

FIG. 4 illustrates rollover head valve 22 in its normally closedcondition for an upright vehicle orientation. The level of liquid fuelin the tank, even at maximum, remains below the level of rollover headvalve 22, leaving rollover float valve 22k in the lowered position awayfrom rollover vent outlet 22i. However, ball head valve 22l iscalibrated to maintain a pressure head in the fuel tank higher than thepressure at which fuel is introduced into the tank during refueling oncethe shutoff control valve 20 has closed. Ball head valve 22l accordinglyremains in the closed position shown in solid lines in FIG. 4 in whichthe head valve vent outlet 22j is blocked by the ball valve element.

Rollover head valve 22 also includes a small bleed vent 22p,illustratively associated with the ball head valve outlet 22j, toprovide a continuous, low volume vent from the fuel tank to the canisterthrough rollover head valve 22 even in the valve closed condition ofFIG. 4. Bleed vent 22p is calibrated to gradually reduce the pressurehead maintained in the fuel tank after the control valve has closed,preferably for a sufficient time to deter further refueling attemptsonce the final shutoff has occurred as described above. In theillustrative embodiment bleed vent is in the order of 0.020 inches indiameter, and temporarily maintains a refuel-preventing pressure head inthe tank after refueling has ceased.

Still referring to FIG. 4, head valve 22l opens as shown in phantom topermit high volume venting of fuel vapor from the tank to the canisterthrough radial vents 22q in the ball-containing nest or cup when thedesired pressure head in the tank is exceeded.

Should the vehicle enter a rollover orientation, or if fuel slosh oroverfill levels rise to rollover head valve 22, rollover float valve 22kis forced against rollover vent outlet 22i as shown in phantom tocompletely close the valve and prevent liquid fuel from leaking to thegcanister.

Referring now to FIG. 5, a first illustrative embodiment of a checkvalve 24 is illustrated for use with the system of FIG. 1. It comprisesa hollow body having an upper cylindrical plug portion 24b inserted inthe lower end of the filler pipe in a sealing, snap-retention fit. Upperplug portion 24b is provided about its circumference with seal beads 24cand a retention flange 24d for that purpose. Check valve 24 furtherincludes a hollow, cylindrical lower valve chamber 24e with a number ofradial vent ports 24f formed about its periphery. The junction of plugportion 24b and valve chamber 24e forms a valve seat 24g. The lower endof valve chamber 24e is closed by an end plate 24h with a central hole24i. A piston-like hollow valve element 24j is located in valve chamber24e for axial movement between valve seat 24g and end plate 24h. Thediameter of valve element 24j is less than the interior dimensions ofthe valve chamber, such that liquid fuel from the filler pipe flowsthrough plug portion 24b, across valve seat 24g, around valve element24j, through radial vents 24f, and into the fuel tank. Valve element 24jis normally biased against valve seat 24g by spring 24k to close thecheck valve. A resilient seal member 24l seals against valve seat 24g inthe closed position, protected from cutting or shearing by a raisedshoulder 24m on the valve element radially exterior of seal 24l. Theupper end of valve element 24j is formed as a rounded, conical flowpilot 24n which projects into plug portion 24b past seat 24g to directfuel flow around the sides of valve element 24j.

Check valve 24 is a one way, positive closing valve which opens to admitfuel from the filler pipe into the fuel tank, but which positivelycloses as soon as the refueling operation terminates and/or the pressurein the fuel tank is equal to or greater than the pressure or weight offuel in the filler pipe. In FIG. 5 check valve 24 is shown in the closedcondition, with seal 24l pressed against valve seat 24g.

Referring to FIG. 5A, when liquid fuel is introduced under pressurethrough the filler pipe into upper plug portion 24b, it forces valveelement 24j against spring 24k toward end plate 24h, opening a flow pathacross valve seat 24g and around valve element 24j through radial vents24f. The rounded, cone-shaped flow pilot 24n directs flow around theoutside of valve element 24j toward the radial vents to reduceturbulence and to generally assist flow through the check valve. As longas the force of fuel against valve element 24j is greater than the forceexerted by spring 24k and the pressure in the fuel tank, check valve 24remains in the open position of FIG. 5A.

To prevent valve element 24j from being held open by the suction effectof liquid fuel flowing through radial vents 24f at the lower end ofcheck valve 24, hole 24i formed in end plate 24h eliminates such suctioneffects by providing a make-up pressure to the lower side of valveelement 24j.

The system and control valve of the present invention accordinglyachieve an onboard control over vapor venting which is particularlyuseful for high pressure refueling using a dynamically sealed fillerpipe, although the control valve has separate utility. The foregoingillustrative embodiments of a system and individual valves according tothe present invention are exemplary in nature, and the invention is notto be limited except as provided in the following claims.

The invention claimed is:
 1. In a vehicle fuel system having a fueltank, a dynamically-sealed filler pipe, and onboard vapor recoveryapparatus, a fuel vapor venting control system comprising:control valvemeans in the fuel tank for venting fuel vapor from the tank to the vaporrecovery apparatus at a first higher rate when the fulel level in thetank is below a first level, at a second lower rate when the fulel levelin the tank reaches the first level, and for closing when a secondhigher fuel level in the tank is reached, the control valve meanscomprising two stage offset valve means responsive to the level ofliquid fuel in the tank, the offset valve means further comprisingliquid level responsive float means, first and second valve meansassociated with the float means, and first and second vent outlet means,the float means being responsive to liquid fuel reaching the first levelto force the first valve means to a position closing the first ventoutlet means, the first valve means further including means for biasingthe first valve means from the second valve means, the float means beingresponsive to liquid fuel level above the first level to force thesecond valve means against the bias of the first valve means intosealing engagement with the second vent outlet means to close thecontrol valve means; valve means in the fuel tank for maintaining apressure head in the tank sufficient to induce filler nozzle shutoffwhen the control valve means is closed and for selectively venting fuelvapor to the vapor recovery apparatus independently of the control valvemeans; and check valve means in a lower end of the filler pipe to closethe filler pipe with respect to the fuel tank between refuelingactivity.
 2. A system as defined in claim 1, wherein the valve means formaintaining a pressure head in the tank further includes bleed means forreducing the pressure head over a predetermined period after the controlvalve means has closed.
 3. A system as defined in claim 2, wherein thevalve means for maintaining a pressure head in the tank includesrollover valve means.
 4. In a vehicle fuel system having a fuel tank, adynamically-sealed filler pipe, and onboard vapor recovery apparatus, afuel vapor venting control system comprising:control valve means in thefilel tank for venting fuel vapor from the tank to the vapor recoveryapparatus at a first higher rate when the fuel level in the tank isbelow a first level, at a second lower rate when the fuel level in thetank reaches the first level, and for closing when a second higher fuellevel in the tank is reached, the control valve means comprising twostage radially offset valve means responsive to the level of liquid fuelin the tank; valve means in the fuel tank for maintaining a pressurehead in the tank sufficient to induce filler nozzle shutoff when thecontrol valve means is closed and for selectively venting fuel vapor tothe vapor recovery apparatus independently of the control valve means;and, check valve means in a lower end of the filler pipe to close thefiller pipe with respect to the fuel tank between refueling activity,wherein the check valve means comprises an axially-operated valveelement including bias means for holding the valve element against avalve seat opposite the direction of fluid flow into the tank, radialvent means selectively opened by the valve element upon introduction ofliquid fuel from the filler pipe into the tank, and means for reducingsuction tending to hold the valve element in an open position caused byflow of fuel through the radial vent means, and wherein the valveelement in the check valve means further includes resilient seal meansforced against the valve seat in the closed position by the valveelement, and shoulder means on the valve element associated with theresilient seal means to limit the force exerted on the seal meansagainst the valve seat by the valve element.
 5. A liquid-responsivecontrol valve for controlling the venting of fuel vapor from a fuel tankto a vapor recovery apparatus in a manner providing a shutoff cue to aperson filling the tank, comprising:a control valve adapted for ventingfuel vapor from the tank to the vapor recovery apparatus at a firsthigher rate when the fuel level in the tank is below a first level, at asecond lower rate when the fuel level in the tank reaches the firstlevel, and for closing when a second higher fuel level in the tank isreached, the control valve comprising two stage offset valve meansresponsive to the level of liquid fuel in the tank, the offset valvemeans comprising liquid level responsive float means, first and secondvalve means associated with the float means, and first and second ventoutlet means, the float means being responsive to liquid fuel reachingthe first level to force the first valve means to a position closing thefirst vent outlet means, the first valve means further including meansfor biasing the first valve means from the second valve means, and thefloat means being responsive to liquid fuel level above the first levelto force the second valve means against the bias of the first valvemeans into sealing engagement with the second vent outlet means to closethe control valve means.
 6. The control valve of claim 5, wherein thefirst and second vent outlet means are radially offset in the controlvalve, and the first and second valve means are radially offset inalignment with the first and second vent outlet means.